[R] convergence error code in mixed effects models

From: Ilona Leyer <ileyer_at_yahoo.de>
Date: Thu, 13 Dec 2007 23:15:31 +0100 (CET)

Dear All,
I want to analyse treatment effects with time series data: I measured e.g. leaf number (five replicate plants) in relation to two soil pH - after 2,4,6,8 weeks. I used mixed effects models, but some analyses didnīt work. It seems for me as if this is a randomly occurring problem since sometimes the same model works sometimes not.

An example:
> names(test)

[1] "rep" "treat" "leaf" "week"
> library (lattice)
> library (nlme)
> test<-groupedData(leaf~week|rep,outer=~treat,test)
> model<-lme(leaf~treat,random=~leaf|rep)
Error in lme.formula(leaf~ treat, random = ~week|rep) :

        nlminb problem, convergence error code = 1; message = iteration limit reached without convergence (9)

Has anybody an idea to solve this problem? Thanks


Ilona Leyer
Conservation Biology
University of Marburg
e-mail: ileyer_at_yahoo.de

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